The invention is directed to a method for the point-by-point and line-by-line recording of rastered images, whereby a modulation signal is superimposed on the image signal that defines the raster density to be recorded in order to avoid discontinuous changes of the raster density.
The invention is also directed to an apparatus for recording rastered images comprising a modulator for combining an image signal and a modulation signal.
In reproduction technology, rastered images are occasionally recorded having a gradual change of the raster density or raster point size, and are referred to as density progressions or uniform density areas having a constant raster density or raster point size. It is thereby required that the density progressions and uniform density surfaces are recorded insofar as possible without disturbing, discontinuous density transitions or density discontinuities, which are also referred to as breaks. Such disturbing breaks, however, cannot always be avoided due to the rastered recording.
German Patent 17 72 367 already discloses a method for recording rastered images wherein a modulation signal is superimposed on the image signal that determines the raster density or, respectively, raster point size in order to avoid disturbing breaks, neighboring raster densities being mixed with the assistance thereof in an overlap region. The mixing of the raster densities within the mixed region occurs according to a statistical distribution.
It has particularly proven disadvantageous in the known method that image islands in which a density skip is not compensated due to a low amplitude of the modulation signal arise due to the statistical mixing corresponding to statistical probability. Beyond this, it is also possible that, given an unfavorable statistical superimposition of an image signal allocated to a uniform raster density with a modulation signal, line-shaped transitions are generated that would not occur without the modulation. It must in fact be presumed that such accidental, visible transition regions are respectively limited to small regions of the image. Particularly in a high-quality reproduction, however, small, discontinuity-like transitions are also perceptible that deteriorate the reproduction quality. Due to the statistical distribution of the modulation signal, beyond this, no reliable prediction can be made about the size and the appearance of such transition regions, since the appearance of specific formations can only be predicted with probability values.